Ablative Preoperative Single-Fraction Radiation Dose Escalation Among Patients With Breast Cancer: A Phase 1...

Area of Science:

• Oncology
• Radiation Oncology
• Breast Cancer Treatment

Background:

• Single-fraction stereotactic partial breast irradiation (sPBI) is an ablative radiotherapy technique.
• Its safety and efficacy in early-stage hormone receptor-positive (HR+) breast cancer with delayed surgery are under investigation.

Purpose of the Study:

• To determine the maximum tolerated dose (MTD) of sPBI through dose escalation.
• To evaluate clinical outcomes, including pathologic complete response (pCR), time to surgery, and toxicity.

Main Methods:

• Phase 1, nonrandomized clinical trial involving patients with HR+, ERBB2-negative, cN0 invasive breast cancer.
• Patients received 30, 34, or 38 Gy of sPBI using MR-guided linear accelerator, robotic radiosurgery, or cobalt stereotactic unit.
• Endocrine therapy was administered, followed by delayed surgery (≤12 months); MTD was assessed via dose-limiting toxicity (DLT).

Main Results:

• MTD was not reached; treatments were tolerable up to 38 Gy.
• Pathologic complete response (pCR) rates increased with dose (35.7% to 66.7%), and pCR with near pCR (npCR) exceeded 93% at 34 and 38 Gy.
• Delaying surgery >9 months post-sPBI was associated with significantly higher pCR and npCR rates (>90%), while higher radiation doses did not show a similar association.

Conclusions:

• sPBI up to 38 Gy demonstrated a low rate of toxic effects and was well-tolerated.
• Delaying surgery beyond 9 months after sPBI and endocrine therapy significantly improved pCR and npCR rates.
• These findings support exploring sPBI as a potential nonsurgical treatment for select early-stage HR+ breast cancer patients.